Camera tube comprising insulated diodes and a resistance layer

ABSTRACT

In a camera tube whose target plate consists of a semiconductor such as silicon, the target plate is provided with a mosaic of discrete domains, each of which forms a rectifying junction with the substrate. the target plate being provided with an insulating layer exposing the domains. A resistance layer of lead monoxide is provided in order to conduct away the electrons incident on the insulating layer.

J anssen Feb. 19, 1974 1 CAMERA TUBE COMPRISING INSULATED DIODES AND A RESISTANCE LAYER [75] Inventor: Peter Johannes Michiel Janssen,

Emmasingel, Eindhoven, Netherlands [73] Assignee: U.S. Philips Corporation, New

York, N.Y.

[22] Filed: Apr. 20, 1972 [21] Appl. No.: 245,782 1 Related u.s. Application Data [63] Continuation-in-part of Ser. No. 18,677, March 11,

1970, abandoned.

[30] Foreign Application Priority Data Crowell 315/10 Crowell 315/12 OTHER PUBLlCATlONS Solid State Abstracts Journal, Vol. 8, No. 1. Abstract No. 61493, article of Pamfilor et al.

Primary Examiner-Martin H. Edlow Attorney, Agent, or Firm-Frank R. Trifari; Carl P.

Steinhauser 57 5 ABSTRACT In a camera tube whose target plate consists of a semi- Mar. 15, 1969 Netherlands 6904045 conductor such as SlIlCOl'l, the target plate Is provIded [52] Us Cl 317/235 R 317/235 N 317/235 NA with a mosaic of discrete-domains,-each of which 313/66 1 forms a rectifying junction with the substrate. the tar- [51] Int Cl H0 15/00 get plate being provided with an insulating layer ex- [58] Fie'ld "317/235 NA posing the domains. A resistance layer of lead monoxide is provided in order to conduct away the electrons [56] Reierences Cited incident on the insulating layer.

UNITED STATES PATENTS 1 Claim 2 Draw Fi m 3,574,143 4 1971 Vratny 252 520 I, g

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CAMERA TUBE COMPRISING INSULATED DIODES AND A RESISTANCE LAYER This application is a continuation of application Ser. No. 18,677, filed Mar. 11, 1970 now abandoned.

The invention relates to a camera tube comprising an electron source and a photo-sensitive target plate to be scanned by an electron beam emanating from said source and formed by a semiconductor substrate provided with an electric contact and on the side to be scanned by the electron beam with a mosaicof'discrete domains, each of which forms a rectifying junction with the semiconductor substrate, the side of the substrate tobe scanned'being'provided with an electrically insulating layer having apertures at the places of said domains, said layer being covered in turn by a thin resistance layer.

Such a camera tube is known from an article in Bell System Technical Journal, Nov. 1968 Nr. 9, pages 1,855 to 1,873. When the target plate of the camera tube described therein is scanned by an electron beam having slow electrons, the scanned area of the target plate is each time stabilized at a potential equal or substantially equal to the potential of the cathode of the electron source. Owing to differences in work functions the electrons in such an electron beam exhibit different speeds. If no resistance layer is provided, the comparatively rapid electrons will-bring the electrically insulatinglayer during the repeated stabilization ata potential which is lower than the cathode potential. As a result of the consequent braking effect of this charged insulating layer the electrons of nominal speed will be disturbed in stabilizing the dorn'ainsorthey will no longer be able to reach said domain. It had furthermore been rays generated within the tube. The layer of lead monoxide'is applied from the vapour'phase, the resistance value of said layer being determined by the conditions of the vapour deposition or by subsequent doping. By the choice of the gas atmosphere and the temperature of the substrate during the vapour-deposition of the lead monoxide this layer may have a high porosity so that the secondary emission of the layer is reduced, which is conducive to the contrast of the tube. The capacitative effect of the resistance layer, which is due only to the layer parts on the domains, can be reduced or even be substantially annulled by using a resistance layer having mains.

One embodiment of a camera tube in accordance apertures at least at the centers of the dowith the invention will be described hereinafter with I construction of the known Vidicon camera tubes, An

elongated, cylindrical envelope l having a glass sheath 2 encloses an exhausted space 6 by an end face 3 having variousthrough connections 4 and a second end face 5 serving as an imput window for the image information light. This space accomodates an electron gun -7, a cathode 8, a control-grid9 and an anode' 10. The

tube, which coils may be replaced by electrodes (not shown) inside the tube for electrostatic focusing and deflection. The target plate 14, to be described more fully hereinafter with reference to FIG. 2, is mounted ve'rsely affect both the contrastand the definition, the

resistance valueper square must not be too low. On the other hand this resistance must not be too high,.since then said braking effect is not sufficiently avoided. In

practice a resistance value per square of 10' to 10'- ohms appears to be satisfactory. Moreover, in view of the capacitative effect in'controlling the tube the resis- The invention has for its object to satisfy these requirements and the tube'ofthe kind set forth is characterized in that the resistance layer consists of lead mon- This material has the advantageous property that the resistance per square of a layer of material can be given the desired value by the conditions of deposition or by a subsequent treatment, while vapour-deposited layers of the material adhere excellently to the support, exhibit a uniform composition and a flat surface. It also has the advantage that it protects the target against):-

in the envelope 1 byclamping its rim between a resilient moonting ring 16, which is in contact both with the input window 5 and the sheath 2 and a second resilient ring 17, which is in contact with the sheath and an end 18 of theelectrodell. The target plate 14, formed by a round disc, is concave on theside facing the window 5 so that the central portion of the disc forms a plate 26 of about 10p. in thickness. A metal ring 19, which serves for the. electric connection, is clamped between the thicker annular circumferential part 27 of the disc 14 and one of the electrically insulating rings 16 or 17. The ring 19 is connected to an electric conductor 20 passed through the wall 2. On the side facing the electron gun 7 the target plate of semiconductor material, in this case silicon, has a mosaic 21, extending up to the portion 27 and formed by domains 22 in a regular array. The material of these domains has a conductivity type opposite that of the material of the further portion (to be termed the substrate hereinafter) ofthe disc 14. The domains 22 may be circular or square and; may have a diameter or a side of about 20a, the central distance between them being about 2511.. The domains form a rectifying junction 23 at a'small depth in the substrate. These junctions have to operate in the reverse direction when the tube is operating. When scanned by slow electrons the domains 22 have therefore to be p-conducting and the substrate has to be nconducting. The side of the target plate 14 provided with the mosaic 21 has an electrically insulating layer 24. This layer does not cover the surfaces of the domains 22 and the thickened rim 27. The insulating layer having a thickness of about 0.5 to 1.0;. preferably consists of an oxide of the semiconductor material of the target plate and in the present case of silica obtained by oxidizing the central portion 26 of the silicon plate. In practice this layer is employed as a mask for establishing the p-conductive domains 22. The silicon substrate covered by the perforated layer 24 is for this end exposed to a dopant, for example, boron so that at the apertures in the oxide layer the silicon becomes 1- conducting to a depth of about 2 the pn-junctions 23 with the substrate being thus formed.

A resistance layer 26 covers the insulating layer 24 and the domains 22. This layer consists of lead monoxide and it has a thickness of not more than 0.2;; and an electrical resistance of about to 10 ohms/square.

The lead monoxide is vapour-deposited in a gas atmosphere of approximately equal parts of oxygen and hydrogen of a pressure of about 6 X 10' Torr. The substrate is kept at about l C during the vapour deposition. These vapour-deposition conditions provide a fairly porous layer of mainly micro-crystalline tetragonal lead monoxide, which exhibits a slight secondary emission. The latter is conducive to the stabilization with a comparatively low beam current and to the prevention of potential image fading. lf-necessary, the electrical resistance of the lead monoxide layer may be given the desired value subsequent to vapour deposition, for example, by doping with oxygen.

In order to avoid capacitative effects it is advantageous to interrupt the resistance layer 25 at the centers of the domains 22, instead of providing an uninter rupted layer. The layer then has apertures at the areas of these mosaic elements. Such an apertured layer may be provided by depositing the material of the resistance layer 25 from the vapour phase across a grating of parallel wires, which grating covers at least the central parts of the domains during the vapour deposition. The vapour deposition is then performed in two different processes, between which the grating-has to be turned through 90. During the two vapour-deposition processes it is preferred to apply equal quantities of material.

What is claimed is:

1. In a camera tube comprising an electron source and a photo-sensitive'target plate to be scanned by an electron beam emanating from said source and formed by a semi-conductor substrate provided with an electric contact and on the side to be scanned by the electron beam with a mosaic of discrete domains each of which forms a rectifying junction with the semicondutor substrate, the side of the substrate to be scanned being provided with an electrically insulating layer having apertures at the area of said domains the improvement comprising covering the latter layer with a layer of lead monoxide having a thickness not exceeding 0.2 .4. and a resistance of 10 to 10" ohms per square, wherein the resistance layer is provided with aperatures at the areas of the central portions of the domains. 

